Ansys Employee
I need to repeat it: The particles and flow will always have the same time so it injects on top of the new time step so that at its ends particle and flow have same time elapsed. Imagine you start from zero the flow time is zero at the first flow time step Fluent will solve for the first time interval for that reason you will particles injected at time 0 [s] as at the end of that time step it has the time 0.001[s].

So this guy: ((0.0 0.0 0.0 0.0 1.0 0.0 0.0001 400.0 1e-11 2.12406e-11 0.56349 0.0 0.0) injection-0:0) with a repeat interval of 0.005

Will inject at 0.0, 0.005, 0.0010. You might notice that i might inject at 0.009 but is due to the fact that the flow time is not 100% equal to 0..09. Particle tracker will rectify that and track the particle again from a fraction of millisecond so that if you look into the particle residence time after 0.010 second you will see consistent behavior.

Again for the particle tracker the time interval / period is important